On other surfaces the lustre is
vitreous. The crystals are usually transparent and colourless, sometimes
with a greenish or rose-red tint. Opaque white crystals of cubic habit
have been called albine; xylochlore is an olive-green variety. The
hardness is 4-1/2, and the specific gravity 2.35.

The optical characters of the mineral are of special interest, and have
been much studied. The sign of the double refraction may be either
positive or negative, and some crystals are divided into optically
biaxial sectors. The variety known as leucocyclite shows, when examined
in convergent polarized light, a peculiar interference figure, the rings
being alternately white and violet-black and not coloured as in a normal
figure seen in white light.

Apophyllite is a mineral of secondary origin, commonly occurring, in
association with other zeolites, in amygdaloidal cavities in basalt and
melaphyre. Magnificent groups of greenish and colourless tabular
crystals, the crystals several inches across, were found, with flesh-red
stilbite, in the Deccan traps of the Western Ghats, near Bombay, during
the construction of the Great Indian Peninsular railway. Groups of
crystals of a beautiful pink colour have been found in the silver veins
of Andreasberg in the Harz and of Guanaxuato in Mexico. Crystals of
recent formation have been detected in the Roman remains at the hot
springs of Plombieres in France. (L. J. S.)

APOPHYSIS (Gr. [Greek: apophysis], offshoot), a bony protuberance, in
human physiology; also a botanical term for the swelling of the
spore-case in certain mosses.

APOPLEXY (Gr. [Greek: apoplaexia], from [Greek: apoplaessein], to strike
down, to stun), the term employed by Galen to designate the "sudden loss
of feeling and movement of the whole body, with the exception of
respiration," to which, after the time of Harvey, was added "and with
the exception of the circulation." Although the term is occasionally
employed in medicine with other significations, yet in its general
acceptation apoplexy may be defined as a sudden loss of consciousness,
of sensibility, and of movement without any _essential_ modification of
the respiratory and circulatory functions occasioned by some brain
disease. It was discovered that the majority of the cases of apoplexy
were due to cerebral haemorrhage, and what looked like cerebral
haemorrhage, red softening; and the idea for a long time prevailed that
apoplexy and cerebral haem